The present invention relates to a color filter substrate used in display devices such as color liquid crystal displays, and to a fabrication method for such a color filter substrate.
Liquid crystal display devices are being widely used in various types of electronic equipment because of their features of being small, thin and light in weight and consuming low power. In particular, active matrix liquid crystal display devices having switching elements are being widely used for office automation equipment such as personal computers, audio-visual equipment such as television sets, mobile phones and the like. In recent years, rapid progress has been made in improving the quality of liquid display devices, such as increasing the size, improving the definition, increasing the effective pixel area ratio (aperture ratio) and improving the color purity.
The structure of an ordinary active matrix liquid crystal display device will be described with reference to FIG. 10. FIG. 10 is a diagrammatic cross-sectional view of a liquid crystal display device.
As shown in FIG. 10, the liquid crystal display device 30 has an active matrix substrate 2 and a color filter substrate 4 opposed to each other, and a liquid crystal layer 6 interposed between these substrates.
The active matrix substrate 2 includes a transparent insulating substrate 8 made of glass and the like, and gate bus lines (not shown) as scanning signal lines, source bus lines 10 as data signal lines, active elements (not shown) such as thin film transistors (TFTs) and transparent pixel electrodes 12 formed on the substrate 8. The plurality of pixel electrodes 12 are arranged in a matrix in the display region.
The color filter substrate 4 includes a transparent insulating substrate 14 made of glass and the like, and a color filter layer 22 composed of red color filter lines 16, green color filter lines 18 and blue color filter lines 20, a light shield layer 26 having a plurality of black matrix portions 24, and a counter electrode (not shown) formed on the substrate 14. The red color filter lines 16, the green color filter lines 18 and the blue color filter lines 20 are provided to correspond to the plurality of transparent pixel electrodes 12 formed in the active matrix substrate 2. The light shield layer 26 is provided so that its black matrix portions 24 exist in the gaps between the color filters and in the frame region.
An example of a fabrication method for the color filter substrate 4 will be described (see Japanese Laid-Open Patent Publication No. 2001-100221).
In recent years, a dry film method has been used for fabrication of a color filter substrate. The dry film method has the advantages that the yield of materials is high and the fabrication cost can be reduced, compared with the spin coat method conventionally used. In addition, by forming the color filter layer and the light shield layer with dry films, the thickness of these layers can be made more uniform.
A fabrication method for a color filter substrate using the dry film method will be described with reference to FIGS. 11A to 11F.
A dry film is composed of a photosensitive resin layer and film supports made of a polyethylene terephthalate (PET) film and the like sandwiching the photosensitive resin layer from both major surfaces. Four kinds of dry films in which red, blue, green and black pigments are respectively dispersed in the photosensitive resin films are used. Typically, the photosensitive resin films are of a negative type.
First, the red dry film, for example, is pressed against the glass substrate 14 with a roller 34 (see FIG. 6) to be stuck on the glass substrate 14, and then the film support is removed, so that a red photosensitive resin layer 16R is transferred onto the substrate 14 as shown in FIG. 11A. This process step is generally performed under heating of the dry film and thus is a thermal transfer step. The transferred red photosensitive resin layer 16R is then exposed to light via a mask 32 and developed, to thereby form the red color filter lines 16 as shown in FIG. 11B.
The same step as that described above is then performed using the green dry film, for example, to form the green color filter lines 18 as shown in FIG. 11C. Likewise, the same step as that described above is performed using the blue dry film to form the blue color filter lines 20 as shown in FIG. 11D. In this way, the color filter layer 22 composed of the red, green and blue color filter lines 16, 18 and 20 is formed.
After the formation of the color filter layer 22, the light shield layer 26 having the black matrix portions 24 given in the gaps between the adjacent color filter lines and in the frame region is formed using the black dry film in the same manner as that for the formation of the color filter lines described above.
The color filter substrate is thus fabricated. FIG. 12 is a partial plan view of the resultant color filter substrate.
In the conventional fabrication method for a color filter substrate described above, for formation of the green color filter lines 18, the blue color filter lines 20 and the black matrix portions 24, the dry films are pressed against the substrate to be stuck on the substrate along a direction parallel to the extension of the stripe-shaped color filter lines (direction of the arrow 70 in FIG. 12).
The reason for the above is as follows. If a dry film is not pressed to be stuck along a direction parallel to the extension of color filter lines previously formed on the substrate, the previously formed color filter lines will block the air existing between the dry film and the substrate from escaping outside, resulting in bubbles remaining between the black matrix and the substrate, and thus causing degradation in display quality such as occurrence of color dropouts.
For the above reason, after formation of one kind of stripe-shaped color filter lines on the substrate, the adhesion direction of a dry film for another kind of color filter lines or black matrix portions to be formed next is limited to only one direction.
For example, in the case of forming color filter lines on a transparent insulating substrate in the shape of a rectangle of 680 mm×880 mm so as to extend along the shorter side of the substrate, once color filter lines of one color are first formed, the adhesion direction of a dry film for color filter lines of another color to be formed next is limited to the direction along the shorter side of the substrate (direction of extension of the color filter lines of the first color). Accordingly, a dry film having a width of 880 mm must be prepared. In the conventional fabrication method, therefore, use of a narrower dry film is not allowed.
In view of the above, an object of the present invention is providing a fabrication method for a color filter substrate that can minimize degradation in display quality and is high in degree of freedom in the adhesion direction of a dry film, such a color filter substrate, and a display device using such a color filter substrate.